fix(admin): preserve form values after save in user and group edit

SvelteKit's default `use:enhance` behaviour calls `form.reset()` after
a successful non-redirecting action, which wipes inputs that use
`value={...}` (property set, not defaultValue). The edit forms now
pass `reset: false` to `update()` so the saved values stay visible
after the success banner appears.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/routes/admin/groups/[id]/+page.svelte

@@ -94,7 +94,10 @@ const ADMIN_PERMISSIONS = $derived([
 			id="edit-group-form"
 			method="POST"
 			action="?/update"
-			use:enhance
+			use:enhance={() =>
+				async ({ update }) => {
+					await update({ reset: false });
+				}}
 			oninput={unsaved.markDirty}
 		>
 			<!-- Group name card -->

frontend/src/routes/admin/users/[id]/+page.svelte

@@ -85,7 +85,10 @@ $effect(() => {
 			id="edit-user-form"
 			method="POST"
 			action="?/update"
-			use:enhance
+			use:enhance={() =>
+				async ({ update }) => {
+					await update({ reset: false });
+				}}
 			oninput={unsaved.markDirty}
 			class="space-y-5"
 		>